Field of the Invention
The present invention relates to a charged particle beam system.
Description of Related Art
Electron microscopes, such as transmission electron microscope (TEM), scanning transmission electron microscope (STEM), and scanning electron microscopes (SEM), are used as means for obtaining structural information about nano-sized materials, devices, and biological samples. Where compositional information on such samples should be obtained, an energy dispersive X-ray spectrometer (EDS) detector is equipped to such an electron microscope.
When EDS analysis is performed using an electron microscope equipped with an EDS detector, the EDS detector is inserted close to a sample placed within a sample chamber. When no EDS analysis is performed, the EDS detector is retracted from the sample chamber. By effecting such operations, where EDS analysis is not made, the electron microscope can be placed in a condition where neither observation of the sample nor exchange of the sample holder is hindered (see, for example, JP-A-2011-153846).
The insertion and retraction of the EDS detector are done under control of an EDS controller and are carried out, for example, when a user selects “IN” and “OUT”, respectively, on the EDS detector via the manual control section of the EDS controller.
In an electron microscope, an electron beam is directed at a sample, and an electron microscope image is formed by detecting secondary electrons or backscattered electrons emitted from the sample, electrons transmitted through the sample, or scattering electrons. When an electron beam is made to hit a sample, there are generated characteristic X-rays attributable to materials or elements constituting the sample. The produced characteristic X-rays have different energy bands for different elements. Therefore, compositional information about the sample can be obtained by detecting the characteristic X-rays.
An EDS system including an EDS detector can detect characteristic X-rays and provide characteristic X-ray intensities which are different for different energy levels. The EDS system can perform various analyses such as point analysis, line analysis, and map analysis combined with scanned images.
In recent years, silicon drift detectors (SDDs) have been put into practical use as EDS detectors and, therefore, higher sensitivity and higher speeds of EDS analysis are being accomplished. An SDD can have an improved detection efficiency by having a larger detector active area so as to increase the detection solid angle.
The detection solid angle, Ω, is given by
  Ω  =                    S        ·        cos            ⁢                          ⁢      θ              L      2      where S is the detector active area, θ is the acceptance angle, and L is the distance from the position of electron impingement on the sample to the center of the detector.
As can be seen from the above equation, in order to increase the detection solid angle of the EDS detector, the detector active area S must be increased, while the distance L must be reduced. Therefore, in order to increase the detection solid angle of the EDS detector, it is desirable to place the EDS detector as close as possible to the sample when the detector is inserted.
However, if the EDS detector is placed closer to a sample, the EDS detector and sample holder may mechanically interfere with each other. Various types of sample holders are available. Different types of sample holders have different shapes and, therefore, it is difficult to place an EDS detector in an appropriate position for analysis.